It is known to determine the steering center of a moving vehicle. This value is important to know for several different advanced vehicle functions, for example vehicle active yaw control. Further, it is important to learn this value as early in the driving cycle as possible so that these vehicle functions may be activated in a timely manner.
One way of determining the steering center of a moving vehicle is the use of an absolute steering wheel angle sensor. An absolute steering wheel angle sensor provides the actual position of the steering wheel at any point in the vehicle""s driving cycle. These sensors are rather expensive averaging approximately $30 each.
On the other hand, relative steering wheel angle sensors average approximately $5 each, making its use desirable to reduce the overall cost of the vehicle. This type of sensor does not provide the absolute position of the steering wheel. Rather, relative steering wheel angle sensors sense movements of the steering wheel only. Unfortunately, the steering center position needs to be determined in each ignition cycle in vehicle""s utilizing this type of sensor. In the beginning of the ignition cycle, the saved steering wheel angle cannot be used since the steering wheel may have been turned while the vehicle was off, making the saved steering wheel angle inaccurate.
It is desirable to use the information that the relative steering wheel angle sensor yields to calculate an accurate absolute steering center value. To yield an accurate absolute steering center value, calculations need to be performed utilizing input from the relative steering wheel angle sensor and other vehicle sensors. Since these calculations are made every time the vehicle starts, and further require specified driving conditions, activation of the advanced vehicle functions can be significantly delayed. Accordingly, there exists a need to provide a low-cost steering wheel sensor that does not delay the calculation of an absolute steering wheel angle and hence activation of the advanced vehicle functions.
The present invention overcomes the disadvantages outlined above by providing a method for determining a steering wheel angle calibration reference value of a vehicle""s steering mechanism utilizing a relative steering wheel angle sensor that can interface with the vehicle""s car area network (xe2x80x9cCANxe2x80x9d) and also receives power directly from the vehicle""s battery.
The purpose of the present invention is to maintain the power supply to the steering wheel angle sensor so that the steering wheel angle value is not lost during power interruptions to the vehicle""s active yaw controller. Rather, only power interruptions to the relative steering wheel angle sensor itself will require updating the steering wheel angle calibration reference value.
The relative steering wheel angle sensor is permanently powered by the vehicle""s battery. If the power to the relative steering wheel angle sensor becomes interrupted, the sensor indicates this to the active yaw controller with a xe2x80x9cdiscontinuity-flagxe2x80x9d via the vehicle""s car area network the next time communication to the controller is reestablished. Typically, communication to the controller will be reestablished as soon as the power supply to the sensor is resumed.
The calibration reference is stored in non-volatile memory and has to be re-determined every time the xe2x80x9cdiscontinuity-flagxe2x80x9d is received from the relative steering wheel angle sensor. The calibration reference is defined as the steering wheel angle sensor signal, which can only be determined while the vehicle is driving down a straight path.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.